Heat filter for intermittent light beam projectors



C. A. HAHN Feb. 2, 1954 2 SheetsSheet 1 Filed March 10, 1948 FIG 3 INVENTOR CHARLES A HAHN BY fl ATTORNEY Feb. 2, 1954 c. A. HAHN 2,667,807

HEAT FILTER FOR INTERMITTEJNT LIGHT BEAM PROJECTORS Filed March 10, 1948 2 Sheets-Sheet 2 CH RLES A. HAHN i W W ATTORNEY Patented Feb. 2, 1954 TED STATES MFFICE ill-EAT L'FILTER {FOR INTERMITTENT EIGHT $.BEAMrPROJEGFE-QRS ,ApplieationyMarch 10, 1948,t-Serial;l\lo.;=14;068

(CL, 88.f17..)

.5 Claims.

.This invention relates todevices ior projecting light beams and is particularly directed to 'gthfi problem of filtering heat rays from a light beam that is to beprojected. .In one oiitsjm- ,portant aspects, the invention is directed to filtering heat rays from a light beam'that. isto be projected intermittently, and in another aspect .it.is..ooncerned.-with provision of a variablelight heat filtering arrangement capable of accurate adjustment to theheatcontent of a light beam with.which it .isto beused, so that the deg-reeof :filteringmay belimitedto that necessary torenuce. theheat content. .oithe I beam to the. desired ,leveL vhileavoidingexcessive filtering action and the unnecessary loss of visible light accompanyin t.

.A typical use of the invention, which may make .full use .of both aspects noted above, is in motion .picture projection, particularly in the professional field, wherein light beams of very highintensity are. used and pictures are, projected from film. that ,is.readily damaged by exposure to light beams having heatcontents inexcess of definite in- .ten/Sities. ,tomarily is produced by a high intensity source, such. as anarc, ina lamphouse arranged tothe rear of the projector -proper,..and.the beam is In-such projectors the light beam cusdirec'tedpast a shutter, that interrupts .it periodically, totheprojector aperture and optical system. Such high intensity beams have heat contents far in excess of. the intensities that filmis capable of withstanding, even during the brief exposure periods necessary ,for projection, so it is universal practice to abstract, heat .from the light. beam'. b fore the beam reachesvthe projector aperture .where it strikes the. film.

"Prior practice .in abstracting heat from. the

lightbeam of a. projector has beento place be tween the l ht source and the projectora heat filter comprising a ,bodyof ceramic or vitreous material having characteristics of. absorbing a highfpercentage of the-heat rays of the light beam andttransmitting a high percentage ,Ofits visible light. Such bodies are constantly exposed to the lightheamsthatthey filter. "Because of the highintensity of lightbeams usedin such projec- 'torsit has become commonpractice to cool such heat-filtersby-directing flows of heat" absorbing fluids over their surfaces, thereby abstracting heat from them at a'faster rate than it can'be dissipatedby radiation, and keeping the filter bodies at temperatures that theyare capable of withstanding.

"Thereisaconstanttrend in intermittent light beamyprojectors toward use of higher lightintensities, and this 'trend has raised the problem solved by the presentinvention. Increase inilight intensity is accompanied by increased intensity of the heat contentof the beam. I-leat. -filter ing material .used in arrangements oi the conventional type described. above have definite limita- ,-tion s;as to the intensity of heat thatit iscapable of absorbing and idissi-paftirrg, and ;the light .intensi-ties ofthebeamat present commonly used, in commercial motion picture projection are such that they are accompanied .1 by heat intensities practically at the .limits of ,the capacities-pf standard filtering assemblies. Increase of light intensity beyond those now employed is accompanied by raising the ,heatzfiltering bodiesrto red heat, resulting in their destruction,bysaggingor cracking.

.{Ihe present invention solves the problem of ad eguate filtering. ,of light ,beamsof intensities beyond those which, a body of ceramic. or.vitreous filtering material constantly exposed to su ch a beam can withstand, by so arranging-thafiltering assem ly hat t e filt nam sriali .expo ed to ;the,1ight beam. only during the periods that the beam actually is being projected, thereby imahodies tothe beam during successive projection periods.

in intermittent,prplectorsequipped.withshutt s a ran ed lbetweenith rli ht. sou c -and th projection aperture, ,such a movable light filter as herein disjclosed may be-combined withthe shutter v structure11 v. so ,mounting one .or ..more

bodies of heat filtering material, according ,to

itheirpe fishutt r th tssaeh abody is interposed-in .thepath. oithe. beamavhen the shutter is.in: a.;pqsition1 to.pass the light beam2 to the p ojector, and removedifrorn .the path .of .the beam when the, shutter 1 obstructs such path. a ,refinement, the. heat filtering ,material may be .so

m unted a tub in r o e i 'th pa o -..the

beam "for only a part of each .projectionperiod whi theshufle js.in., ition,to. i assthe-beam,

1 and. add t onally (the .ifilterins mate ia may .b

adjustable on: the shutter so the relative lengths of thepartsof the-projection periods whenthe lightbeam 'is filtered and unfiltered may be. selected in accordance with theheat content of the particular beam with which an assembly is to be used, and with the permissible level of the heat content of such beam as it enters the projector.

In explanation of the partial and adjustable filtering features of the invention, it may be explained that commercially available ceramic or vitreous material absorbs a certain percentage of the visible light ray content of the light beam as well as a much higher percentage of the heat ray content. With arc beams of the intensities used in standard modern professional projection, filters are used which abstract approximatel'y eighty per cent of the heat content and absorb approximately twenty-two per cent of the visible light rays. These percentages constitute a compromise between the opposed desirable efiects of high heat abstraction and transmission of as much visible light as possible. It will be apparent that in case alight beam of lower intensity is used in a given installation, removal of less than the indicated maximum of eighty per cent of the heat rays may reduce the heat content of the beam to a satisfactory level, so that filtering of the maximum heat content from the beam is accompanied by a greater than necessary loss of light. Consequently, a reduction of the filtering effect is accompanied by an increase in the projected visible light. As indicated, the present invention provides for such reduction from maximum heat filtering by limiting the filtering action to occur during only a part of each projection period. During the remainders of such periods the absorption of visible light due to filtering is avoided, so the total useful illumination of the projected beam is increased.

It is the primary object of the invention to provide a novel method and apparatus for abstracting and dissipating heat from the light beam of an intermittent projector by means of standard ceramic or vitreous filtering material,

which will permit use of light beams having heat intensities beyond those that such materials are capable of withstanding when used in present types of heat filters.

Another object is the provision of a novel heat filtering assembly for the light beam of an intermittent projector, so arranged that the heat filtering material is exposed to the light beam only during periods of actual projection of the beam from the projector.

A further object is the provision of such a novel heat filtering system that requires a minimum alteration of standard type projection equipment to permit installation of the novel heat filtering system instead of conventional heat filtering systems.

A further object is the provision of a novel heat filtering assembly for a projector light beam, providing for partial filtering of a lightbeam to permit saving of visible light ray content of the beam when'heat filtering to the maximum extent isnot necessary.

An additional object is the provision of a novel heat filtering assembly for a projector light beam providing for adjustment of the degree of filtering performed by the assembly.

Another object is the provision of novel structural and mechanical arrangements for accomplishing the desirable heat filtering according to the basic concepts of the invention.

While a great many mechanical means might be used to limit exposure of a heat filtering body to a light beam only during periods of actual projection of such beams by an intermittent projector, such result may be accomplished very con veniently, and with minimum alteration of stand ard projection equipment, by combining one or more movable bodies of heat filtering material with the light beam interrupting shutter of the projector. By arranging the heat filtering bodies in coincidence with the light passing parts of the shutter, the desired result is automatically accomplished in a highly desirable Way.

Such an arrangement is shown in the accompanying drawings wherein:

Fig. 1 is a fragmentary side elevation of part of a projector, embodying the invention, and part of a light source.

Fig. 2 is an elevation of one form of heat filter assembly arranged in accordance with the invention.

Fig. 3 is a sectional view on line 3-3 of Fig. 2.

Fig. 4 is a diagrammatic plan of light source and motion picture projector assembly provided with a filter of the type herein disclosed and showing the relation of such filter to the assembly.

Fig. 5 is a front elevation of a heat filter and shutter assembly modified to permit adjustment of the degree of filtering to be performed by the assembly.

Fig. 6 is a sectional view on line 66 of Fig. 5.

Fig. '7 is a fragmentary sectional view on line 1-4 of Fig. 5.

Describing the drawings in detail and referring first to Fig. 4, a lamp house 1 contains a high intensity light source 2, such as an arc lamp and reflector, arranged to direct a high intensity light beam along the optical axis 3 of a motion picture projector 4.

In Fig. 1 a rear portion of the motion picture projector l is designated 5, and includes structure 6 forming an aperture 1 through which the beam of light is directed to the interior of the projector and upon a film at the aperture. A tubular casing 8 extends rearwardly from the projector, surrounding the axis 3 of the aperture 1, and through which the beam of light is directed upon the aperture. At the rear end of the tubular casing 8 is mounted a shutter housing 9, which is in eccentric relation to the aperture axis, and which has an end opening at I0 in alignment with the aperture 1 for admission of the light beam. The end structure I l of the arc lamp house is disposed in matching alignment with the opening l0, so that the light beam from the arc lamp is coaxial with the opening H! and. aperture 1.

A heat filtering assembly which also operates as a shutter to produce the intermittent character of the light beam necessary for motion picture projection is enclosed by the housing 9, and is shown in detail in Figs. 2 and 3. The assembly is carried by a rotary drive shaft l2, which may be driven in well known manner from the projector mechanism. Adjacent the end of the shaft I2 is a hub i3, having a fiat end surface [4. A circular plate I5 is secured to this end surface M and extends radially and transverse tothe light beam for rotation of an annular portion of the plate, lying between the margin of the surface 14 and the edge of the plate, through the light beam at a point between the opening 19 andthe aperture 1.

Prior practice has been to interpose a heat filtering assembly between the end structure of the lamp house, as H, and the light opening of the shutter casing, as I0, so that the heat filter} ing material of such assembly is constantly exposed to the light beam and filters the heat from the beam before its passage tothe usual shutter izianczgsm i authentication-oi theassembly'rlescribed above.

,ain' dshe :instantrassemblyirtheashutter .plate I5 wzmnprises opaquezsectors" t-i6,;and .oneoramore .cut out; portions; orrgaps .1 I'LZSOZthQtLaSI the plate. rozatates-across the tlightlbeamsthe; lattersalternately .xzis interrupted: :by :ithe. portions I 6 rand passed zby "the gaps H. .The gaps .Ilaare .masked. :by-bodies tauof itransparent :heat'afiltering; material. :Su'ch amaterialzi's well knownincthe .art,s. genera1lyzcompprising -heat :resistiverglasszhaving: a capacityrfor eabsorbing= a :high :I'percentage of .the heat .frequencies, =while' transmitting arhigh percentage of the visible frequencies of light beam .-..directed 1 uponthe. normal .tolits surface.

$.TO': secure @the bodies 18 to 1 .the plate "1| 3, ithe x'lfltt81:1i$ gproviderlwwith a rim atfl which :extends .arcuately across thecutout "regions I 1,:and :prefcerably comprisesra rolled r rim-extending "circumtferentially -.of the whole :-plate,. and projecting rmrially therefrom .on :the side upon .whichzthe ibOdiBS 1 8 :are imounted. 'Preferablyi themutouts terminate aa short distance .einwardly of: the arim, lea.ving.inarrow-sstrips 20 'rbridging their :outer :sides. .To ..the ;central. .portionof xtheaplate 15 is asecuredra keeper plate:2-I,i-havingaazfin;22 spaced -axiallyfromthesurface.of the plate ISrbyafiange 23 and extending along:thereorresponding-iinner margin r24 -.or .each :cutout. ..-Preferablys:the plate -2 I momprises 1a rcirculariplate iscoaxial @with :the -.;plate I5;.and Ltheinnerredgesnf the .cutouts.are .-a.rcuat.e, .and :-.substantially in -'axial registration -With;.the'ifidgefflf'1711B- finr22. .The transparent hodieswlfl :have convex arcuateiouter edges .con-

-tactingitheeinner. surface oftth'erim I9. and bear- :ingzupon :the :bridge aportion 2 0; whi1e their inner --edges=.are. concave .-.and.:engaged..between the fin .21 and thez-su'rfaice;-of ;plate t5. .Therplates l5, 2 I: zare detacha-blysecured :together as by screws 25. The side edgesaofithebodies I8 maybe se-' cured-by radiallyidisposed 2 bars 26 having base flanges 21 secured detachably to the plate I5, and flanges I28- overlying 'the =edge portionsof the bodies. Such :bars g-prevent "relative angular movement between the bodies I8 and the assemblyfoiplates I5, 2|.

I'Inaview of the relatively high heat absorption 'zoftheheat' filtering'bodies I18,- due to .their infierru'ptionr'of heat 'rays, and the portions I6 of theshutter, plate due to their interruption or" the entiredightbea'm, means isprovided formovair'over'the -surface of the-assembly tocool it. Thisimay be accomplished by a fiow of coolfluid'producedby'a conventional cooling ar- Tangement,.orby providing theplate I5 with air moving blades. "In'the present assembly these are shown as=anglebars ifl disposed on chords of the circular margin ofatherplate I5, andhaving webs .30 .projecting axially and "serving as fan blades during rotation of the assembly. Inlet and vent openings are provided in the shutter housing 9 in any suitable arrangement.

It will be readily appreciated that in addition to protection of the heat filtering material during periods when the beam is cut ofi from the projector, provision of a moving transparent heat filter for a light beam greatly reduces concentration of heat absorption per unit area, as compared to a stationary heat filtering body, an area of which corresponding to the cross section of the light beam, is exposed to the beam and absorbs the entire abstracted heat of the beam.

Additionally it will be apparent that the distribution of heat absorption throughout the annular region of the shutter assembly that passes through thesbeam reduces-aha: volumerflowzwtc :or. cooling :rfluid 1: necessaryito :prerent excessive heating :ofe-theassembly, *zsoirthatcadequatezeo'ol- 'ing mayrbemccomplishedtby fanblades mounted on theshutteriaplate. .I'inal1y,-.:the:combination of shutter, .moving rs-heat filterwand'rlfiuid-nnoving .means in'ratsingle iassembly :provirles imaximum eificiencyiin ruse aofipower consumed. llhesesiaatures icooperate:..inzpermitting ;use;offlightgbeams 10 iprojectionrperiod and(additionally tDLIJEOYfdf-IOI variationiofzthe length ofzsuchiparts eitherprojecti'on .periods to permitzadjustmenttozthe heat content ofaaparticular lightzbeam whichzcontent -requires?lessdilteringzthan :the'imaximurmot-which the assembly is capable. The modified shutter :andtfilter assembly of Figs.:5t'to'..7L.providesgfor ysuch partial filtering :and adjustment.

The assembly igmounted on ;a-..hub s lllsincludiling a circular :plate 4 I @the smarginal portion :of

which is provided with azcircumferential' flange 42 of reduced thickness providing ashoulder :43. Shutter blades 44 vproject radially fromzthe edge of "the flange at'v angular intervals, .beingzseparated by gaps '4 5: that constitute:lightsapassing apertures. At their ends ithe blades-1.14.4 carry'ia circular rim 46 having an.' internal: shoulderxdl that tprovides: a surface. on a; common planeawith the corresponding surface iOfthe fiange'ifl.

I annular. keeper plate:48" issecured-1to "the rim :46, as by screws- 49,-.overlying the shoulder 41 and with it-forming a:groovewherein-rare received the outer u marginal -portions ot-sector shaped plateelike bodies 50 :of the vitreousuor ceramic heat filtering material. The grooves aare so. related to the thickness of these bodies 50 that the latter-are slidable, for angulanmovement relative tothe; axis-ofthe hub.

A keeper plate 5 I is. secured.- to the hub .plate Washers overlie thelattenplate L;The .keeperplate 5| .ahas :anaxially-ofiset annular flange 55 that surroundstthe body of fthe ihub plate AI and contacts :the'shoulder 43 and surfaceaof .theifiange 42. ..This;fiange 55 isiprovided withgaps'56 .that:.receive the inner :end

:portions. of. the filter bodies 50, as best shown in Figs. Band '7. By rotatingthe keeperplateiM on. the :hub plate AI the angular .position of the .filter bodies 50 .is-.changed relative; to the light seeps-"4510f the shutter, so thatthe' extent to :which "they mask suchgapsmay he selected. J-The se- .lectedpositionsof thetfilter bodieszrmaylbeifiired by tightening the screws 52.

' It will be seen that the invention is based on the concept of moving a body or bodies of filtering materials through the light beam in synchronism with periods during which the light beam is being projected, and protecting the filtering material against absorption of heat by removing it from the beam during periods when the beam is not being projected. In this manner the commercially available and commonly used vitreous or ceramic light filtering material, which has definite limits of temperature to which it can be raised, can successfully be used with beams of light having such heat content intensities that the material cannot be continuously exposed to them without damage by excessive heating. This provision for extension of the range of beam intensities is definitely related to the ceramic or vitreous material referred to throughout the foregoing description, since such material is present considered as providing ideal filterin being of uniform light-transmitting quality throughout its area as distinguished from screens .of opaque material, such as metal, provided with apertures for transmitting limited parts of the light beam. Such screens simply reduce the intensity of the light beam and reduce its heat content only in proportion to reduction of the visible light. Consequently, such screens do not perform a true filtering action. As used herein, the term filtering material is limited to material of the character indicated and excludes perforated or foraminous screens of opaque material.

Intermittent filtering of a light beam is not necessarily restricted to intermittent projectors, but may usefully be employed in continuous projection of a light beam by alternately filtering such beam and passing it unfiltered. Ihis may be accomplished by interposing a body of filtering material in the path of the beam intermittently, and in intervening intervals permitting the beam to be projected unfiltered. Conveniently this can be accomplished by rotating through the path of the beam a body of the filtering material having gaps that pass through the path in alternation with such material. By making relatively adjustable the areas of the gaps and filtering material, the adjustable features described above may be utilized to obtain accurate adjustment of the heat content of a light beam that is to be projected continuously.

I claim:

1. In apparatus for projecting a beam of light intermittently including a shutter through the path of the light beam and having a light gap that passes through such path to provide intermittent light-passing periods; a heat filtering body of material having properties of transmitting and blocking passage of high percentages respectively of visible and heat frequencies of such light beam mounted'on said support, and means for adjusting the position of said body to selectively vary an area of the gap covered thereby.

2. In apparatus for projecting a beam of light intermittently including a shutter comprising a plate rotatable through the path of the light beam and having a .gap adapted to pass through such path for providing intermittent light passing periods; a heat filtering body of material having properties of transmitting and blocking passage of high percentages respectively of visible and heat frequencies of such light beam mounted on said plate and angularly adjustable relative movable to it about the axis of rotation for covering a. selected portion of the gap.

3. In apparatus for projecting a beam of light intermittently, a heat filter and shutter assembly comprising a shutter blade, a gap and a body of heat filtering material all arranged to pass through the path of the light beam, and means for adjusting the relative positions of the heat filtering body material having properties of transmitting and blocking passage of high percentages respectively of visible and heat frequencies of such light beam relative to the gap and shutter blade for varying the relative efiective areas of the gap and body of heat filtering material.

4. In apparatus for projecting a beam of light intermittently including a rotatable shutter comprising alternate blades and gaps adapted to pass through the light beam successively as the shutter rotates to provide intermittent lightpassing periods; a heat filtering body of material having properties of transmitting and blocking passage of high percentages respectively of visible and heat frequencies of such light beam associated with each said gap, said bodies being mounted on the shutter and angularly adjustable about its axis of rotation to cover selectively variable areas of the gaps with which they respectively are associated. i

5. In apparatus for. projecting a beam of light intermittently including a rotary shutter comprising a plate rotatable through the path of the light beam and having therein a gap adapted to pass through such path to provide intermittent light-passing periodsya second plate rotatable with the first plate and angularly adjustable relative thereto about the axis of rotation, and a body of heat filtering material in fixed angular relation to said second plate and angularly adjustable with it forselectively varying an area of the gap covered by said body. 7 CHARLES A. HAHN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,385,162 Tillyer July 19,1921 1,406,802 Young Feb. 14, 1922 1,525,346 Warren Feb. 3,1925 1,537,315 Lang May 12, 1925 1,884,730 Kindelmann Oct. 25, 1932 1,949,477 Kindelmann Mar. 6, 1934 2,082,488 Friebus June 1, 1937 2,207,050 Clemens July 9, 1940 2,228,479 OGrady Jan. 14, 1941 2,269,494 Tillyer Jan. 13, 1942 FOREIGN PATENTS Number Country Date 480,267 Great Britain Feb. 21, 1933 

